Cationic latices and method of preparing same



United States Patent Oifice 3,399,159 Patented Aug. 27, 1968 3,399,159CATIONIC LATICES AND METHOD OF PREPARING SAME Carlos M. Samour,Wellesley Hills, Mass., assignor to The Kendall Company, Boston, Mass.,a corporation of Massachusetts N Drawing. Continuation-impart ofapplication Ser. No. 457,526, May 20, 1965. This application Feb. 6,1967, Ser. No. 614,002

15 Claims. (Cl. 26029.6)

ABSTRACT OF THE DISCLOSURE A process for preparing polymericdispersions, free of surfactants or conventional dispersing agents, andin which the polymer is cationically charged, which comprisespolymerizing at a controlled rate in an acid medium a mixture ofmonomers comprising a nitrogen-containing monomer and an alkyl acrylicester. A redox catalyst is used, and the monomers are introduced intothe system at a rate which is within the range of proportions desired inthe finished polymer, to avoid the formation of coagulum.

This application is a continuation-in-part of my copending applicationSer. No. 547,526, filed May 20, 1965, now abandoned, which in turn in acontinuationin-part of my application Ser. No. 329,309, filed Dec. 9,1963, now abandoned. It relates to new cationic polymeric compositions,and to processes for producing such systems. In one specific embodiment,the invention relates to a new polymeric dispersing system in which thedispersing agent is a cationic copolymer, and to the utilization of sucha dispersing system for the preparation of cationically-stabilizedtwo-component polymeric latices.

In a second specific embodiment of the invention, the reaction iscarried out in such a way that a one-component, self-dispersed polymeris formed, in which the cationic dispersing group is an integral part ofthe polymeric molecule.

Polymeric latices are for the most part conventionally produced by anemulsion polymerization process, in which monomeric materials arepolymerized while they are dispersed in an aqueous medium by means of asurface active agent. The surface active agent may be anionic in nature,such as soap flakes or sodium lauryl sulfate. Alternatively, it may beof a nonionic type as represented by various ethylene oxide derivatives,or by polyhydroxy compounds, or it may be cationic, as represented byalkyl ammonium halides. Cationic active agents are not entirelysatisfactory when used as sole emulsifying agent, and are frequentlycombined with a nonionic agent for improved performance. Thepolymerization of monomeric materials is also frequently effected in thepresence of water-soluble protective colloids or stabilizing agents. Anyof the above emulsifying agents leads to the presence of awater-sensitive ingredient in the final polymeric latex. For latexutilizations wherein wet strength is desirable, as in paper coatings,non-woven fabrics, certain pressure-sensitive adhesive tapes, and thelike, the presence of such water-sensitive material is deleterious.

Although it has heretofore been proposed in US. Patent 3,108,979 toprepare stable dispersions by copolymerizing certain amino alcoholesters with a variety of other monomers in the absence of conventionalemulsifiers, it has now been found that best results can be achieved inthe present invention only by copolymerizing very restricted classes ofmonomeric materials, and further that only certain carefully controlledconditions may be used during the polymerization of these monomericmaterials. The polymerization must be initiated with a water-solubleredox catalyst; peroxides and persulfates, which are commonly employedfor polymerizations are ineffective for carrying out the presentinvention in the absence of a reducing agent. In addition,polymerization must be continued throughout the period during which themonomeric materials are being added to the reaction mixture, and therelative proportions of the monomeric materials to each other must bemaintained within a defined range throughout this period; the entireamount of individual monomeric materials cannot be added to thepolymerization mixture one after the other, nor can the entire amount ofmonomeric material be added to the polymerization mixture beforepolymerization has been initiated.

It is, therefore, an object of this invention to preparecationically-stabilized polymeric dispersing systems of a newcomposition, wherein the dispersing polymer is essentially insoluble inwater and may be precipitated from dispersion by charge neutralization.

In one aspect of the invention, termed a one-component system, only asingle species of polymer is prepared, the polymer being self-dispersedin an aqueous medium by reason of the presence of cationic dispersinggroups in the polymer molecule, and being useful as a binder or bondingagent for nonwoven fabrics, for example, and as a component ofpressure-sensitive adhesive compositions. In another aspect of theinvention, called a twocomponent system, the self-dispersed polymer isemployed as the dispersing agent for polymerizing additional monomers,different from the first, so that the final aqueous dispersion containstwo species of polymer, only one of which contains cationic dispersinggroups in the polymer molecule. The two-component system is also usefulas a binder or bonding agent for nonwoven fabrics and as a component ofpressure-sensitive adhesive compositions. In both aspects of theinvention, no watersoluble dispersing agent is employed.

An additional object of this invention is the utilization of suchpolymeric latices for the preparation of bonded nonwoven fabrics and ofpressure-sensitive adhesive tapes. A more specific object of theinvention is the preparation of a new polymeric dispersing systemcomprising a positively charged copolymer of one nitrogen-containingsaltforming organic monomer with at least one ethylenicallyunsaturatedorganic monomer of a class set forth below. It is also an object of thisinvention to prepare a polymeric dispersing system wherein themole-ratios of the monomers are so chosen as to facilitate thepolymerization therein of other monomers with the formation of laticesmarked by low viscosity and small particle size. Still another object ofthe invention is to prepare a polymeric dispersion of unusually lowviscosity, consisting of a single polymeric component in whichdispersing groups are an integral molecular part of said component.Further objects of the invention will appear in the followingdescription thereof.

1 have found that new cationically-stabilized polymeric aqueousdispersions, having utility in various technical applications, may beprepared by means of a new polymeric dispersion system in which thedispersing copolymer contains certain especially effective mole ratiosof reactants. In general, the polymeric dispersing systems, thetwo-component dispersions prepared therefrom, and the one-componentspecies are characterized by a low surface tension. Specifically, mypreferred dispersing system is prepared from at least two monomers. Oneof said monomers is a nitrogen-containing ethylenically-unsaturatedorganic monomer capable of forming a salt with acids: such compounds maybe a vinyl pyridine such as 2-, 4-, or 5-vinyl pyridine; a substitutedvinyl pyridine, wherein one of the previous vinyl pyridines containsadditional, preferably loweralkyl, substituents on the ring or on thealpha position of the vinyl group, such as 2-methyl-5- vinyl pyridine;2, 3, 4-trimethyl-5-vinyl pyridine; 3, 4, 5, 6-tetramethyl-2-vinylpyridine and the like: or an unsaturated organic amine of the generalformula:

R1 B2 I H,: -COX-A(NHA)y-N\ wherein:

R is hydrogen or a methyl group, X is O or NH,

A is an alkylene group selected from the class consisting of dimethyleneor isopropylene,

Y is zero or one,

R is a hydrogen atom or a saturated alkyl group of not more than fourcarbon atoms, and R is a saturated alkyl group of not more than fourcarbon atoms, being tertiary butyl when R is hydrogen,

and wherein the total number of carbon atoms in both R and R does notexceed four.

Typical examples of this class of salt-forming amino compounds aredimethylaminoethyl methacrylate, tertiarybutylaminoethyl methacrylate,and amide-amines such as N-(dimethylaminoethyl) acrylamide.

This salt-forming compound is copolymerized with at least oneethylenically-unsaturated acrylic monomer, from the class represented bythe general formula where R is a hydrogen atom or a methyl group, and Ris a saturated alkyl radical. In the case where a polymeric dispersingsystem is formed for the purpose of carrying on the polymerization ofother monomers to form a twocomponent system, in which the cationicpolymer first formed acts as a dispersing agent, R is a saturated alkylradical of not more than four carbon atoms. In the case of aone-component system, in which all of the monomers are copolymerized toform a single polymeric species containing the salt-forming monomer asan integral part of the polymer, R is a saturated alkyl radical of notmore than eight carbon atoms.

It has been found that in the preparation of stable aqueous dispersionsof water-insoluble cationic polymers in satisfactory yield according tothe methods set forth herein, any substantial deviation from thelimitations set on these alkyl groups will result in failure. Thelimitations are therefore critical.

Mixtures of more than one such ethylenically-unsaturated monomer may bepolymerized with the salt-forming monomer to form ternary dispersingagents, or agents of even higher order, provided that the dispersingsystem meets the criteria of insolubility set forth more freelyhereinbelow.

The ethylenically unsaturated acrylic comonomer should be in major part,preferably not less than 90 mole percent, chosen from the class setforth immediately above, or mixtures of monomers selected therefrom. Inorder to impart to the dispersion polymer certain properties oftoughness, rigidity, or cross-linking reactivity, a part of the majormonomerpreferably not more than mole percentmay be replaced by someother ethylenically-unsaturated monomer including vinyl esters such asvinyl acetate, vinyl laurate, and vinyl stearate; vinyl ethers such asvinyl methyl ether, vinyl ethyl ether, and vinyl butyl ether;di-unsaturated monomers such as diethylene glycol diacrylate, ethyleneglycol diitaconate diallyl phthalate, divinyl benzene and the like;acrylic and methacrylic acids, acrylamide and methacrylamide,acrylonitrile, itaconic acid, hydroxyethyl acrylate and methacrylate,and hydroxypropylacrylate and methacrylate.

The preparation of these cationically-stabilized polymeric dispersions,whether it involves the preparation of a cationic polymeric dispersionand the subsequent polymerization of other monomers therein, as in thetwocomponent system, or whether it involves the preparation of aone-component system containing a single species, selfdispersed polymer,is conveniently carried out in an acidified aqueous medium, as is setforth in detail in the examples below. In general, a pH of between 1.0and 3.5 has been found most effective, with a preferred range of 1.5 to2.5. Such a pH may be realized by the use of highly dissociated acidssuch as hydrochloric, nitric, sulfuric, or formic acids, or other strongacids which have a dissociation constant below 5.0 and preferably below3.0.

The catalyst system which must be employed in the present invention, aspointed out above, is a redox catalyst consisting of an oxidizing agentand a reducing agent, both of which have some water solubility. Theoxidizing agent may be, for example, ammonium persulfate, hydrogenperoxide, tertiary butyl peroxy maleic acid, tertiary octylhydroperoxide, 2,S-dimethylhexyl-Z-S-dihydroperoxide, methyl ethylketone peroxides, and the like. The reducing agent may be ascorbic acid,dihydroxy maleic acid, reducing sugars and the like, together with ametal ion capable of existing in two valence states such as ferrous,cuprous, vanadyl, stannous, and the like. Such redox catalyst systemspromote rapid initiation of polymerization, which minimizes theaccumulation of unreacted monomer in the dispersion. Such anaccumulation is undesirable, since unreacted monomer is usually asolvent for partially polymerized material, so that the presence ofdispersed but unreacted monomer leads to the formation of agglomeratedparticles and even to coagulum. Coagulum in a latex dispersion isunusable polymer, and not only reduces the yield of effective polymerdispersion but must be removed by filtration or settling before thedispersion can be used as, for example, a binder for nonwoven fabrics.The undesirability of coagulated polymer in a dispersion is especiallyevident in processes where the polymer is being continually formed andcontinually removed from the system. Such a continual process isrecognized as especially advantageous when the preparation of apolymeric dispersion is coordinated with its utilization. For suchreasons, it is essential that the monomers be maintained in properproportion to each other at all times during the preparation of thepolymeric dispersion. If the cationic monomer is present in thepolymerizing system for an appreciable time in a mole ratio in excess ofthe limits set forth herein, a polymer will be formed which iswater-soluble or water-sensitive, which will defeat the primaryobjective of enhanced resistance to the effects of water. If thenon-cationic monomer is present in excess, it will dissolve or swell thedesired polymeric particles already formed, and coagulum will result.

In general, in preparing a polymeric dispersing system intended for usein the further polymerization of other monomers to form a two-componentpolymeric latex, the dispersing systems I have found most useful arethose in which the mole fraction of the nitrogen-containing monomer inthe dispersing system is between 0.1 and 0.5: that is, my preferredpolymeric dispersing compositions are those in which the mole ratio ofnitrogen-containing monomer to the ethylenically-unsaturated monomerlies between 1 to 9 and l to 1. Dispersions outside of this preferredrange either are less efficient in the polymerization of subsequentlyadded monomers if the mole fraction of nitrogen-containing monomer isbelow about 0.1, or tend to become undesirably water soluble if the molefraction goes much above 0.5.

The following Examples 1, 2, 3 and 4 will illustrate the preparation oftypical dispersing systems in accordance with one phase of the processesof this invention.

EXAMPLE .1

A stable cationic emulsifying system was prepared by the slow additionof a mixture of 31.45 grams (0.2 mole) of dimethylaminoethylmethacrylate and 68.54 g. (0.6 mole) of ethyl methacrylate to a stirredand heated (70 C.) solution of 189 ml. of 7.4% hydrochloric acid in1,679 ml. water. During the addition of the monomer mixture there wasalso gradually added 12 ml. of 3% aqueous hydrogen peroxide and ml.water in which were dissolved 0.1 g. of ferrous ammonium sulfate and 0.4g. ascorbic acid. The addition of the various ingredients was spreadover a period of about 50 minutes, after which stirring was continuedfor 15 minutes with the temperature maintained at 70 C.

A smooth and stable emulsifying system resulted, with a surface tensionof only 43.1 dynes per centimeter, rendering the system eminentlysuitable for the rapid and efficient dispersion of other monomericcompounds for polymerization purposes.

EXAMPLE 2 The procedure of Example 1 was repeated except that themonomeric mixture consisted of 1 mole of 2-vinyl pyridine and 3 moles ofethyl methacrylate. A stable dispersing system was formed which had asurface tension of 46.5 dynes per centimeter.

EXAMPLE 3 The procedure of Examples 1 and 2 was repeated except that themonomeric mixture consisted of 1 mole of tertiary butylaminoethylmethaciylate and 3 moles of ethyl methacrylate. The stable dispersingsystem had a surface tension of 45.9 dynes per centimeter.

EXAMPLE 4 A stable cationic emulsifying system was prepared according tothe general procedure of Examples 1, 2, and 3, except that the monomermixture consisted of 3.73 parts of 4-vinyl pyridine, 10.05 parts ofmethyl methacrylate, and 1.22 parts of ethylene glycol dimethacrylate.The mole ratios of the ternary composition were 3 moles (70%) of primaryacrylic ester, 1 mole of saltforming monomer, and 0.2 moles (5%) ofmodifying ester. The pH of the dispersing system was 1.2, and thesurface tension 49.5 dynes per centimeter.

Although considerable latitude may be exercised in the choice ofsalt-forming monomer and ethylenicallyunsaturated co-monomers,nevertheless certain criteria must be fulfilled in order to produce asatisfactory polymeric dispersing system according to this invention. Aforemost criterion is that the positively charged copolymer shall be atrue dispersion, and not a solution. In general, dispersion is marked bythe appearance of a stable, essentially nonstratifying, milkily turbidaqueous phase: unsatisfactory soluble copolymers display little or nohaze or turbidity in an aqueous phase. The transition from asatisfactory dispersion state to an unsatisfactory solution state may bebrought about by improper selection of the comonomer, as the followingexperiment illustrates.

The procedure of Example 2 was repeated except that 3 moles of vinylethyl ether, instead of ethyl methacrylate, was copolymerized with 1mole of 2 vinyl pyridine. A clear solution was obtained, of awater-soluble polymer, which displayed little or no dispersing powereven though its surface tension was only 37.8 dynes per centimeter. Thesolution was of no value as a dispersing system.

I have found that the homopolymers of the above-categorizednitrogen-containing salt-forming monomers are not suitable alone asdispersing agents for further polymerization of other monomers accordingto this invention, due to the fact that such homopolymers in salt formare water soluble. For a true dispersion, it is necessary that thesalt-forming monomers be copolymerized with a second monomer ormonomeric mixture, and that the second monomer be of such limited watersolubility that the copolymer is insoluble in water, but readilydispersed therein in a positively charged salt form. As a quick test ofthe efficacy of a particular copolymer salt as a dispersing system, itis convenient to shake together about 2 volumes of the system and 1volume of toluene in a separatory funnel. A suitable copolymer willdisperse the toluene into a relatively stable emulsified form in theaqueous phase, whereas an unsatisfactory copolymer, such as a vinylpyridine-vinyl ethyl ether copolymer, will result in rapid reseparationof the toluene from the aqueous phase.

In addition to the fact that water-soluble copolymers or homopolymersare not efiicient dispersing agents, it should be recalled that anobject of this invention is to prepare cationic polymeric systemswherein the dispersing agent is relatively insensitive to water. Thedispersing copolymer, as prepared in Examples 1, 2, 3 and 4, hasessentially polymerized to as great an extent as it is going to polymer126.

That is, when this aqueous copolymer dispersion is used for thepolymerization of other monomers, as in the twocomponent system, thereis little or no reaction between the dispersing copolymer and the addedmonomers, apart from the possibility of a modest amount of graftpolymerization. The added monomers polymerize among themselves to form asecond and essentially independent copolymeric species. Since thedispersing copolymer is a separate species in the final latex, it shouldbe relatively water-insoluble if the final latex is to bewater-insensitive.

In addition to the choice of monomers to be copolymerized to form asatisfactory dispersing system, the moleratio of salt-forming monomer tothe other monomer must be maintained within certain limits as pointedout above in order to insure water-insolubility. The salts of thenitrogen-containing monomer are in general more water-soluble than theethylenically-unsaturated monomers with which they are copolymerized: inthis respect, they tend to solubilize the copolymer to the extent towhich units derived from such salt-forming monomers are found in thecopolymer.

Using a mole ratio of 1 salt-forming monomer to between 1 and 9 moles ofother monomers, generally satisfactory results are obtained. When theratio of salt-forming monomer to other monomer exceeds about 1 to 1,however, an unsatisfactory soluble copolymer is liable to result, asseen from the following experiment.

The procedure of Example 1 was repeated except that 4 moles of 2-vinylpyridine were polymerized with 3 moles of methyl methacrylate. Theresulting system had a pH of 1.2 and a surface tension of 41.1 dynes percentimeter, but it was clear and transparent and had no dispersing valuedue to its water solubility.

It will be apparent to one skilled in the art that the desiredinsolubility of the dispersing copolymer will also depend upon thesolubilising tendency exerted by the nature of the comonomer, as well ason the mole fraction of salt-forming monomer. Thus although 2-vinylpyridine and ethyl methaciylate in a 1 to 3 mole ratio produced asatisfactory dispersing system (Example 2), replacement of the ethylmethacrylate by the more soluble vinyl ethyl ether, maintaining the samemole ratio, led to a copolymer which was soluble and of little value asa dispersing agent. The true test of an effective dispersing systemaccording to this invention is the formation of a turbid dispersion ofan insoluble copolymer in a positively-charged salt form.

The following 14 exemplary dispersing systems, prepared according to theprocess of this invention, have been found to function satisfactorily inthe process of polymerizing other unsaturated monomers. In all cases,the pH of the aqueous phase was between 1.0 and 3.5, the temperaturebetween 70 C. and C., and a redox catalyst as in Example 1 was used.Generally, the concentration of dispersing polymer is about 2% to 10%,preferably around 5%, in the acid aqueous medium.

7 EXAMPLES 548 Three moles of methyl methacrylate with 1 mole ofdimethylaminoethyl methacrylate, 2-vinyl pyridine, or 4- vinyl pyridine;1, 3, or 7 moles of ethyl methacrylate with 1 mole of dimethylaminoethylmethacrylate; 3 moles of ethyl methacrylate with 1 mole of 2-vinylpyridine or tertiary butyl aminoethyl methacrylate; 1 or 3 moles ofibutyl methacrylate with 1 mole of dimethylaminoethyl methacrylate; 3moles of ethyl acrylate with 1 mole of 2- vinyl pyridine; 3 moles ofisopropyl methacrylate, isobutyl methacrylate, or tertiary butylmethacrylate with 1 mole of dimethylaminoethyl methacrylate.

The size of the alkyl group attached to the acrylic or methacrylic esterappears to play a significant role in the efficiency of the dispersingsystem. For example, when 2 moles of hexyl methacrylate were polymerizedwith one mole of dimethylaminoethyl methacrylate, the monomers failed toform a dispersing system. Neither was a dispersing system formed bytrying to react 3 moles of styrene with 1 mole of dimethylaminoethylmethacrylate.

In the case where a cationically-stabilized polymeric dispersing systemis formed for the polymerization of other monomers therein, as in atwo-component system, the acrylic and methacrylic esters which form thedispersing polymer are limited to not more than four carbon atoms in thealkyl ester group.

As indicated above, a water-soluble copolymer also does not effectivelydisperse other added unsaturated monomers so as -to allow theirpolymerization. The following dispersing systems were found to beunsatisfactory due to their water-solubility:

Three moles of vinyl ethyl ether with 1 mole of dimethylaminoethylmethacrylate or 2-vinyl pyridine; 3 moles of n-butyl vinyl ether with 1mole of dimethylaminoethyl methacrylate; 3 or moles of vinyl acetate, or3 moles of vinyl butyrate, with 1 mole of 2-vinyl pyridine.

A cationically-charged polymeric dispersion system prepared inaccordance with this invention may be used in the preparation ofaddition polymers of ethylenically unsaturated monomers capable ofaddition polymerization to form homopolymers or copolymers. Examples ofsuch unsaturated monomers include: esters of ethylenic' ally-unsaturatedacids, such as alkyl acrylates, meth' acrylates, maleates, citraconatesand itaconates in which the alkyl ester groups, for example, may containfrom 1 to 18 carbon atoms and which may contain such sub stituents ashydroxy, cyano, or alkoxy groups such as hydroxyethyl methacrylate,cyanoethyl acrylate, meth' oxyethyl acrylate, and the like; amido,including n-alkyl amido, derivatives of such acids, including amicacids, imides, diamides and ester amides, such as acrylamide, n-butylacrylamide, maleamic acid, t-butyl maleamic acid, n-butyl itaconimide,dibutyl itaconamide, the ethyl ester of maleamic acid, and the like;vinyl esters such as vinyl acetate, vinyl propiona-te, and vinyllaurate; vinyl esters such as methyl vinyl ether, ethyl vinyl ether, andisobutyl vinyl ether; vinyl chloride and vinylidine chlor' ide; styrenesand substituted styrenes such as beta methyl styrene and the like; anddienes such as butadiene and substituted derivatives thereof, isoprene,chloroprene, and the like; vinyl pyrrolidone and the like. The choice ofmonomers will depend on the balance of properties which it is desired toachieve in the particular end-use to which the polymeric latex is to beput. In a preferred embodiment, this monomer is an alkyl ester ofacrylic or methacrylic acid or mixture thereof in which the alkyl groupcontains from 1 to 8 carbon atoms.

EXAMPLE 19 Preparation of two-component polymer dispersions A monomericmixture of 65.85 parts by weight of ethyl acrylate, 30.30 parts 2-ethylhexyl acrylate, and 3.85 parts of hydroxyethyl methacrylate, containing0.115 part of dodecyl mercaptan, was added slowly to 191 parts of acationic-active dispersing system composed of a dispersion of a 1 moleto 3 mole copolymer of dimethylaminoethyl methacrylate and ethylmethacrylate, prepared as in Example 1. The concentration of thecopolymer in the dispersing system was 5% by weight.

During the polymerization there was also added at intervals a total of 7parts of hydrogen peroxide of 3% concentration, together with 0.1 partof ferrous ammonium sulfate and 0.4 part of ascorbic acid in 10 parts ofwater, at a rate which kept the reaction temperatures at between 25 C.and 43 C. The resulting cationic polymeric dispersion had a pH of about1.5, a'solids content of about 36%, and a Brookfield viscosity at 50r.p.m. of 68 centipoises. The milky white dispersion was free fromcoagulum and large particles, and was readily coagulated to a gel by theaddition of ammonia.

Films cast from such a dispersion and eoagulated while still wet byexposure to ammonia vapor are after drying tough and coherent, and donot lose their strength when Wet. The tensile strength and modulus ofbinders prepared according -to this invention may be increased by theinclusion of conventional cross-linking monomers in the polymericdispersion, or by the addition of crosslinking agents such as melamineformaldehyde.

EXAMPLE 20 To 50 parts by weight of the dispersing system of Example 1there was added gradually 25 parts of vinyl acetate, whilethe dispersionsystem was maintained at 70 C. During the addition of the vinyl acetatethere was added simultaneously 14 parts of an aqueous solutioncontaining 0.07 part of ferrous ammonium sulfate and 0.28 part ofascorbic acid, as well as 3 parts of 3% hydrogen peroxide. Stirring at70-80 C. was continued for 30 minutes after the vinyl acetate additionwas completed.

The resulting cationic polyemric dispersion had a pH of about 1.8 and aBrookfield viscosity at 20 r.p.m. of 10 centipoises. It was free fromcoaglum and large particles, and was readily coagulated to a gel by theaddition of ammonia.

EXAMPLE 21 A cationic dispersing system was prepared as follows. Theaqueous system consisted of 847 parts of H 0, 87 parts of 7% HCl, and 2parts of 3% hydrogen peroxide. To this there was added, gradually andwith stirring over the course of 30 minutes, a mixture of 36.6 parts(0.258 mole) of butyl methacrylate and 13.4 parts (0.085 mole) ofdimethylaminoethyl methacrylate. The ratio of butyl methacrylate tosalt-forming monomer was 3 to l. Simultaneously with the monomers therewas added 5 parts of a solution of 0025 part of ferrous sulfate and 0.05part of ascorbic acid in water. One third of the way through theaddition of the monomers, another 2 parts of 3% hydrogen peroxide wasadded, and a like amount two-thirds of the way through the addition. Thetemperature was maintained at 70 C. for 1 hour, with stirring, tocomplete the formation of the polymeric dispersion system.

To 200 parts of the above polymeric dispersion system heated at C. therewas added with stirring a mixture of 63 parts of ethyl acrylate and 31parts of methyl methacrylate, simultaneously with the addition of 7parts of 3% hydrogen peroxide, and a solution of 0.1 part ferrousammonium sulfate and 0.4 part ascorbic acid in 10 parts of water.Addition was complete in a period of 15 minutes. The resultingdispersion was heated to 83 C. for 30 minutes, with stirring. Theresulting dispersion contained no coagulum. It had a pH of about 1.3, asurface tension of 39.7 dynes per centimeter, and a Brookfield viscosityof 16 centipoises at 20 r.p.m. The solids content was 34.0% versus atheoretical content of Essentially identical results were obtained whenthe ratio of n-butyl methacrylate to dimethylaminoethyl methacrylate inthe dispersion system was increased to 6.9 to l, and then to 9 to 1:that is, in each case the dispersing system served to promote thesubsequent polymerization of an ethylenically-unsaturated monomericmixture without the formation of any precipitate or coagulum.

It has been my general experience that when a dispersing system isformed from an acrylic ester and a saltforming monomer in a mole ratioexceeding 9 to 1, polymerization of other ethylenically-unsaturatedmonomers in such a system does not proceed smoothly, a certainpercentage of the yield is lost in unusable coagulum, and the resultingpolymeric dispersion always requires laborious filtration before beingusable as a coating or binder latex. My preferred range, therefore, isthe use of not more than 9 moles of acrylic ester to 1 mole ofsalt-forming comonomer.

In addition to the variables set forth above, the ordinary variables andauxiliary procedures commonly used in the art of preparing and usingpolymeric dispersing systems also apply to the process of thisinventionfIncreased temperature promotes more rapid reaction, smallerparticle size, and consequently lower surface tension, as does efficientagitation. The use of finely-divided inert material, such as fullersearth, is frequently useful in obtaining better polymeric dispersionspresumably by surface adsorption of the reactants with a consequentlarge surface area exposure. The second polymer of the two-componentspecies is generally prepared at a concentration of from 20% to 45%, aconvenient and conventional working range for commercial polymericlatices. Ordinarily, about one part of polymeric dispersing agent isused with from about 10 to 20 parts of main polymer, so that the amountof cationic salt-forming monomer present is no more than about 10 molepercent of the total monomers present in both species of polymer.

Utilization of cationically-stabilized polymeric dispersions in thepreparation of pressure-sensitive adhesives The polymeric dispersionsdescribed herein are useful in the preparation of pressure-sensitiveadhesive addition polymers. The adhesive polymer produced is dispersedin the aqueous medium. Adhesive tapes may be prepared therefrom bycoating a suitable backing with the dispersion and evaporation of theessentially aqueous medium in which the polymer is dispersed. Thecationicallycharged polymer of the dispersing system preferably is alabile complex that is destroyed upon removal of the aqueous medium. Thedried adhesive polymer as deposited directly from the dispersion isfreeof watersensitive components such as may be present in the case ofadhesive polymers prepared byconventional emulsion polymerizationsystems. Accordingly, laborious and expensive procedural steps for theremoval of water-sensitive emulsifying or dispersing agent are obviatedby this invention.

Pressure-sensitive adhesive polymers are rubbery, ela'stomeric polymerswhich by themselves exhibit the balance of tack, adhesion and cohesioncharacteristic of pressure-sensitive adhesives. Pressure-sensitiveadhesive polymers may be synthesized by the addition polymerization ofcertain ethylenically unsaturated monomers. Examples of these arehomoacrylate polymers derived from alkyl acrylates averaging from about4-12 carbon atoms in the alkyl ester groups; copolymers of saidacrylates and a minor amount of copolymeriza'ble acrylic monomer such asacrylic acid; and copolymers of C to C alkyl acrylates or methacrylatesand from minor to substantial amounts of a copolymerizable N-alkyl amidoderivative of an ethylenically-unsaturated monocarboxylic and/oralpha-beta dicarboxylic acid. In the case of the latter copolymers, thenumber of carbon atoms in the alkyl ester groups of the acrylates ormethacrylates, the number of carbon atoms in the N-alkyl or alkyl estergroup of EXAMPLE 22 A cationically-charged dispersion system wasprepared according to the general procedure of Example 1, using a 6.9 to1 mole ratio of ethyl acrylate to dimethylaminoethyl methacrylate.

To parts ofthis aqueous dispersing medium there were added, in a l to 1to 4 mole ratio, 50 parts of a mixture of N-alkyl maleamic acids, ethylarcylate, and butyl acrylate.

The N-alkyl maleamic acids were prepared by a amidating maleic anhydridewith a mixture of alkyl amines marketed by Rohm and Haas as Primene 8lR.This commercially available product is reported to be a mixture ofN-t-alkyl primary amines containing the structural element andconsisting principally of C to C alkyl amines. As reported in the Rohmand Haas Brochure SP-33, this mixture has a neutral equivalent of 191,corresponding to an alkyl amine having an average of about 12 carbonatoms.

The N-alkyl maleamic acid, ethyl acrylate, and butyl acrylate monomerswere copolymerized in the ethyl acrylate-dimethylaminoethyl methacrylatedispersion system at 70 C. using a hydrogen peroxide-ferrous ammoniumsulfate-ascorbic acid redox catalyst. The final aque ous polymericdispersion had a pH of 1.8 and a Brookfield viscosity at 50 rpm. ofabout 12 centipoises.

This low viscosity rendered the polymeric dispersion unsuitable forspreading on a backing to form an adhesive tape. However, the additionof a small amount of methyl ethyl ketone directly to the aqueouspolymeric dispersion rapidly thickened the dispersion to a viscosity ofseveral thousand centipoises. In this phase it was readily spread on apolyester film and allowed to dry. Drying was accompanied by thespontaneous evolution of HCl. The resulting film-backed adhesive masshad excellent tack, and the combination was useful as an adhesive tape.

Utilization of cationical-ly-stabilized polymeric dispersions in thepreparation of bonded non-woven fabrics Cationically-stabilizedpolymeric dispersions prepared in accordance with this invention havebeen found to be advantageous in the bonding of webs of fibers to formnon-woven fabrics. Since the dispersion is cationic, the fibrous web,saturated with the dispersion, may be treated with an alkaline agent,such as ammonia, to coagulate the binder in situ, thus minimizing themigration of binder to the web surfaces which accompanies the drying ofnonwoven fabrics saturated with conventional latices. Additionally,since the dispersions of this invention are stabilized by acationically-charged polymer, the system does not contain soap,surfactants, or other low molecular weight water-soluble agents commonlyused in the preparation of conventional latices. Thus the bond betweenfiber and polymer is less sensitive to deterioration when the non-wovenfabric is Wet with water, and a high ratio of wet-strength to drystrength is attained as illustrated in the following example.

ethylhexyl acrylate, and hydroxyethyl methacrylate was prepared in acationically-charged polymeric dispersion of 1 l ethyl methacrylate anddimethylaminoethyl methacrylate, as set forth in Example 19 above.

This dispersion was applied directly to a lightly-needled web of rayonfibers prepared on a *Rando-Webber. The add-on was 25% added solids onthe weight of the web. While still wet, the web was exposed to ammoniavapor to coagulate the dispersion to a firm, relatively non-migratorygel, and dried. The dry weight of the bonded web was 70 grams per squareyard.

Tensile strengths were measured on inch-wide strips using the InstronTester. The dry machine-direction strength was 4.37 pounds, wetmachine-direction strength 3.47 pounds, a ratio of 79% wet to dry. Thedry crosswise strength was 4.23 pounds and the wet crosswise strengthwas 3.13 pounds, a wet-to-dry ratio of 74%. These ratios of wet-to-drystrength are unusually high for bonded nonwoven fabrics. The bondednon-Woven. fabric appeared uniformly impregnated with binder throughoutits thickness, and could not be delarninated.

Dispersion polymers comprising the lower esters, ethyl and methyl, ofacrylic and methacrylic acids are particularly advantageous in thepreparation of nonwoven fabric binders when employed in a ratio of 2 to5 moles of ester to one mole of salt-forming monomer. The secondpolymeric species, constituting the principal binder, may be a mixtureof acrylic or methacrylic esters containing from 1 to 8 carbon atoms inthe ester group, to provide the desired combination of toughness andstrength without brittleness. Polyvinyl acetate is another eminentlysuitable binding agent. To increase the modulus of the binder,acrylonitrile may be mixed with an acrylic ester, and bydoxyethylmethacrylate may be added for cross-linking purposes. Other desirablepolymeric dispersions prepared in accordance with this invention willreadily suggest themselves to those skilled in the non-woven art.

One-component system The cationic monomers employed in preparingcopolymer dispersions for use as dispersing systems may also be employedin preparing one-component self-dispersed polymers. In such case, thecationic monomer must be employed in amounts from 2 to 10 mole percentof the total monomers present, the remainder being an acrylic monomer ofthe general formula:

where R, is hydrogen or a methyl group and R is a saturated alkylradical having 1 to 8 carbon atoms. As in the case of the dispersingpolymer of the two-component system, up to 10 mole percent of theacrylic monomer may be replaced by another ethylenically unsaturatedmonomer.

In the preparation of my single-component cationic polymeric systems,the same conditions of acidic aqueous medium, catalysts, etc., pertainas in the case of my two-component systems.

It has been my experience that when the polymerization is conducted witha non-redox catalyst and with all of the monomers either initiallypresent or added sequentially without regard to mole ratios,ditliculties are encountered in initiation of polymerization and information of coagulum, or of water-sensitive polymers, or both. As setforth above, the result of temporarily exceeding the range of moleratios or percentages set forth herein is the formation of undesiredpolymeric species.

The improved process of this aspect of the invention, the one-componentsystem, therefore, comprises maintaining the ratio of cationicsalt-forming monomer to the remaining monomer or monomers within thespecified range throughout the polymerization and ensuring thatpolymerization, initiated by a redox catalyst system, is continuedthroughout the period during which the monomeric materials are beingadded to the reaction (i.e. polymerization) mixture.

12 The following examples will illustrate various methods for practicingthe process of this phase of my invention.

EXAMPLE 24 An aqueous acidic medium was prepared by placing 1040 partsby weight of water and 137 parts of 7.4% aqueous HCl in a reactionvessel, which was then purged with nitrogen and heated to C., afterwhich 8 parts of 3% aqueous H 0 were added with vigorous stirring. Withcontinued stirring and in a nitrogen atmosphere there weregraduallyadded separately but simultaneosuly 10 parts of a solution of0.05 part of ferrous ammonium sulfate,and.0.2 part of ascorbic acid in10 parts of water, together with 647 parts of a mixture of the followingmonomers:

Dodecyl mercaptan, as terminating agent to control molecular weightAfter about 160'parts, or one-quarter of the monomer mixture had beenadded, an additional 8 parts of 3% H 0 were added, said addition beingrepeated after onehalf, three-quarters, and all of the monomer had beenadded. Agitation and heating were then continued to complete thereaction.

The result was a stable and homogeneous dispersion of acationically-charged polymer, in which about 3% by weight (1.8 molepercent) of the polymer was derived from the nitrogen-containing,salt-forming monomer. The polymeric dispersion was self-dispersed, freefrom surfactants, and was readily coagulated by amomnia. It had a pH of1.7, a solids content of 33%, and a Brookfield viscosity at 50 r.p.m.(spindle #2) of only 11 centipoises, making it suitable for readypenetration into and saturation of nonwoven webs, even without furtherdilution as is frequently necessary with relatively viscous conventionalpolymeric dispersions.

EXAMPLE 25 Using the same general procedure as in Example 1, with thesame catalyst in the same proportions, the following mixture of monomerswas added to a solution of 21 parts of concentrated sulfuric acid(95-98%) in 1,000 parts of water at 0.:

Parts Ethyl acrylate 250 N-butyl acrylate 630 Hydroxyetbyl methacrylate20 Acrylonitrile 70 2-vinyl pyridine 30 EXAMPLE 26 A mixture of 1 moleethyl acrylate, 2 moles butyl acrylate, and 0.068 moledimethylaminoethyl methacrylate was prepared, the mixture containingabout 2.2 mole per cent of the cationic salt-forming monomer.

Fifty parts by weight of the mixture was added continuously and slowly,over a period of 30 minutes, to a polymerization medium comprising asolution in 189 parts water of 2.2 parts phosphoric acid and 0.63 partof tertiary butyl hydroperoxide, the pH of the solution being about 3.0and the temperature being maintained at 70 C. A separate reducingsolution of 0.05 .part of ferrous ammonium sulfate and 0.2 part ascorbicacid in 10 parts of water was also added continuously'to thepolymerization medium over the same period of time as the monomermixture. Polymerization began promptly after addition of monomers wasbegun, a blue colored dispersion being formed initially and becomigwhitish in color as additional polymer was formed. The polymerizationmedium was stirred at 70 C. for about one hour after all of the monomerand reductant solution had been added. The finished stable dispersioncontained approximately 20% by weight of water-insoluble polymerself-dispersed in the aqueous medium.

EXAMPLE 27 .The procedure of Example 26 was repeated except that thetertiary butyl hydroperoxide was initially mixed with the monomermixture instead of with the water, and there was substituted for theascorbic acid 0.1 part of dihydroxymaleic acid. The results were thesame as in Example 26.

EXAMPLE 28 The procedure of Example 26 was repeated except that thetertiary butyl hydroperoxide was omitted and there wasused instead 0.1part of t-butyl peroxy maleic acid mixed with the monomer mixture. Theresults were the same as in Example 26.

EXAMPLE 29 The procedure of Example 26 was repeated except that thetertiary butyl hydroperoxide was omitted and replaced by 015 part ofcumene hydroperoxide in the monomer mixture. The results were the sameas in Example 26.

EXAMPLE 30 The procedure of Example 26 was repeated except that thetertiary butyl hydroperoxide was replaced by 0.06 part of hydrogenperoxide in the polymerization medium, and an additional 0.06 part ofhydrogen peroxide was added after one-half of the monomers had beenadded, and except that the reducing solution was replaced by a solutionof 0.05 part cuprous chloride and 0.2 part ascorbic acid in 15 parts ofwater. The results were the same as in Example 26.

EXAMPLE 31 The procedure of Example 26 was repeated except that thetertiary butyl hydroperoxide was omitted and replaced by a solution of0.5 part ammonium persulfate in parts of water, which was addedcontinuously to the polymerization mixture while the monomers were beingadded, and except that the reducing solution was added intermittently insmall portionsinstead of being added continuously. The results were thesame as in Example 26.

EXAMPLE 32 The procedure of Example 26 was repeated except that insteadof dissolving 0.63 part of tertiary butyl peroxide in the polymerizationmedium, only 0.3 part of this peroxide was dissolved in 10 parts ofwater, which was added continuously over the same period of time as themonomers. In addition, instead of adding the reducing solutioncontinuously, there was mixed with the monomer mixture 0.05 part ofvanadyl acetyl acetonate, and a solution of 0.3 part ascorbic acid in 10parts of water was added intermittently in small portions. The resultswere the same as in Example 26.

EXAMPLE 33 14 temperature was held at 28 to 32 C. The results were thesame as in Example 26.

The various redox catalyst systems illustrated in Examples 2633 are alsoetfective in preparing dispersions of polymers of the type described inExamples 1-4 useful in a two-component system, in which the mole ratioof the acrylic ester type monomer to cationic salt-formingmonomerisfrom1z1t09z1.

As set forth above, the preparation of a self-dispersed cationicpolymeric dispersion by the gradual addition of the reactive monomersto'an aqueous acidic system in which polymerization is rapidly initiatedand steadily promoted by a redox catalyst results in a high degree ofreaction completion and a minimum amount of loss due to coagulum, sincethe monomers do not accumulate to excess in the presence of partialpolymers. The reaction is relatively slow at temperatures below about 5C. and at about 100 C. the aqueous medium may tend to boil. Althoughpolymerization may be conducted at these extremes of temperature, mypreferred reaction temperature is 60 to C. which, with the gradualstepwise addition of monomer to the reacting system, promotes a smoothand complete reaction. The method set forth above may be modified by thecommon methods customarily employed in the art of preparing polymericdispersions. As is expected, increased temperature promotes more rapidreaction, smaller particle size, and consequently lower surface tension,as does efiicient agitation. The addition of finely-divided inertadsorbent material, such as fullers earth, is frequently useful inobtaining better polymeric dispersions, presumably by surface adsorptionof the reactants with consequent large surface area exposure.

The self-dispersed polymer is generally prepared at a concentration offrom 20% to 45%, a convenient and conventional working range forcommercial polymeric latices. Ordinarily, about 2% to 10% of'the polymeris made up of groups derived from the nitrogen-containing, salt-formingmonomer, with a preferred range of 3% to 5%, although this figure may bevaried.

Having thus described my invention, I claim:

1. The process of preparing a self-stabilized polymeric dispersion freefrom surfactant in which the dispersed polymer is water-insoluble andcontains cationic groups which comprises:

introducing into an aqueous medium at pH between about 1.0 and about 3.5(I) at least one monomer selected from the class consisting of (1) alkylacrylic esters and alkyl methacrylic esters in which the alkyl groupcontains up to eight carbon atoms and (2) mixtures thereof with up to 10mole percent of other ethylenically unsaturated monomer and (II) atleast one nitrogen-containing salt-forming monomer selected from theclass consisting of vinyl pyridines, substituted vinyl pyridines, andcompounds having the structure R1 CHz=COX-A(NHA) N wherein R is hydrogenor a methyl group; X is oxygen or NH; A is an alkylene group selectedfrom the class consisting of dimethylene and isopropylene; Y is zero orone; R is a hydrogen atom or a saturated alkyl group of not more than 4carbon atoms; R is a saturated alkyl group of not more than 4 carbonatoms, the total number of carbon atoms in R and R combined notexceeding 4, R being a tertiary butyl group when R is a hydrogen atom,initiating polymerization in said medium by means of a redox catalystsystem, and continuing polymerization throughout the period during whichsaid monomers are being introduced into said medium, and maintaining theamount of said one monomer present in said medium within the range 90 to98 mole 15 percent and the amount of said salt-forming monomer presentin said medium within the range 2 to 10 mole percent throughout theperiod during which said monomers are being introduced into said medium,to form a water-insoluble cationicallycharged polymer consisting of saidmonomer polymerized within said ranges of proportions, said dispersionforming a water-insensitive deposit when dried. 2. The process asclaimed in claim 1 in which the saltforming monomer is vinyl pyridine.

3. The process as claimed in claim 1 in which the saltforming monomer isdimethylaminoethyl methacrylate. 4. The process of preparing a polymerdispersion free from surfactants in which the dispersed polymer iswaterinsoluble and contains cationic groups, which comprises:introducing into an aqueous medium at a pH between about 1.0 and about3.5 (I) at least one monomer selected from the class consisting of (1)alkyl acrylic esters and alkyl methacrylic esters in which the alkylgroup contains up to four carbon atoms and (2) mixtures thereof with upto 10 mole percent of other ethylenically unsaturated monomer and (II)at least one nitrogen-containing salt-forming monomer selected from theclass consisting of vinyl pyridines, substituted vinyl pyridines, andcompounds having the structure wherein R is hydrogen or a methyl group;X is oxygen or NH; A is an alkylene group selected from the classconsisting of dimethylene and isopropylene; Y is zero or one; R is ahydrogen atom or a saturated alkyl group of not more than 4 carbonatoms; R;, is a saturated alkyl group of not more than 4 carbon atoms,the total number of carbon atoms in R and R combined not exceeding 4, Rbeing a tertiary butyl group when R is a hydrogen atom,

initiating polymerization in said medium by means of a redox catalystsystem, and continuing polymerization throughout the period during whichsaid monomers are being introduced into said medium, and maintaining themolar ratio of said one monomer to said salt-forming monomer within therange from 1:1 to 9:1 in said medium throughout the period during whichsaid monomers are being introduced into said medium to form awater-insoluble cationicallycharged polymer consisting of said monomersplymerized within said range of ratios, said dispersion forming awater-insensitive deposit when dried.

5. The process of preparing a polymer dispersion of at least twodiiierent water-insoluble polymers, at least one of which containscationic groups, said dispersion being free from surfactant, whichcomprises preparing a first polymer dispersion as claimed in claim 4,introducing into said first polymer disperison at least onewater-insoluble ethylenically unsaturated monomer, and polymerizing thelast said monomer in said medium in the presence of said first polymeras the sole dispersing agent to form a water-insoluble polymer of thelast said monomer.

6. The process as claimed in claim 5 in which the last said monomer isselected from the class consisting of alkyl esters of acylic andmethacrylic acid in which the alkyl group contains from 1 to 8 carbonatoms.

7. A single species polymeric composition comprising an aqueousdispersion of a cationically-cha'rged waterinsoluble copolymer of atleast two monomers, one of said monomers being a salt-formingnitrogen-containing monomer selected from the class consisting of vinylpyridines, substituted vinyl pyridines, and compounds of the classrepresented by R1 R1 CH =-OOX-A-(NHA)y-N wherein R is hydrogen or amethyl group; X is O or NH; A is an alkylene group selected from theclass consisting of dimethylene and isopropylene; Y is zero or one; R isa hydrogen atom or a saturated alkyl group of not more than 4 carbonatoms; R is a saturated alkyl group of not more than 4 carbon atoms, thetotal number of carbon atoms in R and R combined not exceeding 4; Rbeing a tertiary butyl group when R is a hydrogen atom: together with atleast one monomer selected from the class consisting of alkyl esters ofacrylic and methacryilc acids wherein the esterifying alkyl groupcontains not more than eight carbon atoms and mixtures of said esterswith up to 10 mole percent of other ethylenically unsaturated monomer,the polymeric composition containing between 2 and 10 mole percent ofthe nitrogencontaining monomer, said dispersion forming awaterinsensitive deposit when dried.

8. A polymeric composition suitable for dispersingethylenically-unsaturated monomers comprising an aqueous dispersion of acationically-charged water-insoluble copolymer of at least two monomers,one of said monomers being a salt-forming nitrogen-containing monomerselected from the class consisting of vinyl pyridines, substituted vinylpyridines, and compounds of the class represented by wherein R ishydrogen or a methyl group; X is O or NH; A is an alkylene groupselected from the class consisting of dimethylene and isopropylene; Y iszero or one; R is a hydrogen atom or a saturated alkyl group of not morethan 4 carbon atoms; R is a saturated alkyl group of not more than 4carbon atoms, the total number of carbon atoms in R and R combined notexceeding 4; R being a tertiary butyl group when R is a hydrogen atom;together with at least one monomer selected from the class consisting ofesters of acrylic and methacrylic acids wherein the esterifying alkylgroup contains not more than four carbon atoms,

said copolymer comprising from one unit to nine units derived from saidacrylic ester for each unit derived from said salt-forming monomer, saiddispersion forming a water-insensitive deposit when dried.

9. A cationically-stabilized polymer latex comprising at least twodifferent polymeric species, the first of said species comprising acationically-charged water-ins0lub1e copolymer of at least onesalt-forming nitrogen-containing monomer selected from the classconsisting of vinyl pyridines, and compounds of the class wherein R ishydrogen or a methyl group; X is O or NH; A is an alkyl group selectedfrom the class consisting of dimethylene and isopropylene; Y is zero orone; R is a hydrogen atom or a saturated alkyl group of not more than 4carbon atoms; the total number of carbon atoms in R and R combined notexceeding four, R being a tertiary butyl group where R is a hydrogenatom; together with at least one monomer chosen from the classconsisting of alkyl esters of acrylic and methacrylic acids wherein theesterifying alkyl group contains not more than four carbon atoms;wherein said copolymer comprises from one unit to nine units derivedfrom said acrylic ester for each unit derived from said salt-formingmonomer,

the second of said polymeric species being a waterinsoluble polymer ofat least one ethylenically-unsaturated compound, said second polymericspecies being maintained in stable dispersed form by saidpositively-charged first species, said latex forming a water-insensitivedeposit when dried.

10. The product according to claim 9 wherein said second polymericspecies is a polymer selected from the class consisting of polymerizedacrylic and methacrylic alkyl esters containing from 1 to 8 carbon atomsin the ester group.

11. The process as claimed in claim 1 in which said nitrogen containingsalt-forming monomer is a vinyl pyridine.

12. The process as claimed in claim 1 in which the nitrogen-containingsalt-forming monomer is a substituted vinyl pyridine.

13. A single species polymeric composition as claimed in claim 7 inwhich the salt-forming nitrogen-containing monomer is a vinyl pyridine.

14. A single species polymeric composition as claimed in claim 7 inwhich the salt-forming nitrogen-containing monomer is a substitutedvinyl pyridine.

15. A stable, self-dispersed aqueous polymeric dispersion, free fromsurfactants, and in which the polymer 2 is cationically charged, whichcomprises a water-insoluble copolymer comprising:

2 to 10 mole percent of a salt-forming monomer selected 18 from theclass consisting of vinyl pyridines and substituted vinyl pyridines, 80to 98 mole percent of at least one monomer of the general formula 5 CH=(|JOOORi R wherein R is hydrogen or a methyl group and R is an alkylgroup containing between 1 and 8 carbon atoms, and zero to 10 molepercent of other ethylenically-unsaturated monomers, said polymericdsipersion being in an aqueous medium of a pH of between 1.5 and 3.5,said dispersion forming a water-insensitive deposit when dried.

References Cited UNITED STATES PATENTS 2,880,116 3/1959 Alps et al.3,108,979 10/1963 LeFevre et al.

OTHER REFERENCES Ind. Eng. Chem. 47 863-6 (1955 Pritchard et a1. (TPI A58). 5

MURRAY TILLMAN, Primary Examiner.

J. L. WHITE, Assistant Examiner.

